1. Field of the Invention
The present invention relates to a method for evaluating stability for repeated readout of an optical disc and to an information reproduction apparatus.
2. Description of the Related Art
At present, optical discs such as CDs (Compact Discs), DVDs (Digital Versatile Discs), BDs (Blu-ray Discs; trademark) are used to record or reproduce various types of content. When compared to other media, optical discs are more suitable for archival applications such as long-term storage of content and repeated readout. Therefore, in optical discs, read stability is very important, including the ability to maintain a certain level of signal quality even after readout is repeated any number of times, and also including the ability to prevent recorded content from being lost. Generally, optical discs are required to maintain stability even after readout is repeated about one million times.
However, when readout is actually repeated about one million times in order to evaluate stability for the repeated readout of an optical disc, a laser beam must be projected onto the disc continuously for at least several hours. This is inefficient and is likely to deteriorate the laser.
In view of the above, Japanese Patent Laid-Open Publication No. 2003-6941 discloses a method for evaluating the read stability of an optical recording medium. Specifically, in this method, a linear approximate expression for the relationship between the common logarithm of the number of readout times and a read power is determined based on measurement values obtained by repeating the readout at a plurality of read laser beam powers. The read stability when the readout is repeated at any read laser beam power is evaluated by means of the approximate expression.